Application of heat transfer labels to containers such as plastic bottles for consumer products is common. Generally speaking, heat transfer labels to be applied are arranged in serial fashion on a long strip or web of material such as paper. A release layer, which may be a wax, a lacquer, a combination of the two, or another substance, is disposed on the web for printing. During the labeling process, plastic bottles (or other articles) to be labeled traditionally have had their dyne level modified by being moved past an air/gas flame directed toward the path of the bottles. This causes the surface of the bottles to oxidize, which advantageously alters the surface tension characteristics of the bottle so that a label can be applied more effectively. Attempts to replace treatment heating with an alternative have not proven cost effective and so flame pre-treatment has persisted even though it uses an open flame.
The label web is heated by being passed over a pre-heat plate and/or a heated platen to begin to melt and thus soften the material of the release layer. Each bottle then passes an applicator station, wherein a label on the web is aligned with and progressively transferred from the web and onto the surface of the bottle. A transfer roller insures uniform contact between the label and the bottle. The label sticks to the surface of the bottle and some of the material of the release layer remains on the label.
Each labeled bottle is then traditionally moved past a post-treatment station, where it is again subjected to a post-treatment air/gas flame. The heat of the post-treatment flame melts the wax and/or lacquer or other material from the release layer, causing it to flow over the underlying label thereby forming a clear glossy protective layer on the label and fixing the label securely on the surface of the bottle. This is sometimes referred to as “glossing out” the label. The post-treatment flame also tends to “burn out” defects such as air bubbles beneath labels and defects in labels so that the defects can be detected more easily by a downstream quality control vision system.
More recently, plastic bottle and label chemistries have been developed that eliminate the requirement to pre-treat the bottles to create surface tension before applying heat transfer labels. This is a welcome development for bottle labelers because supplying pre-treatment heat in the form of an air/gas flame in a labeling machine introduces risks, complexity, and costs that are undesirable. For instance, the relatively open flame can present hazards to workers and, in the event of a machine jamb, can result in melted bottles or even fires. With the newly developed chemistries, however, the air/gas burners in the pre-treatment station are not needed and can be eliminated.
Even where the need for pre-treatment heating is eliminated, post-treatment heating to gloss out the applied labels and burn out defects is still highly desirable. However, since an undesirable air/gas flame is not required for pre-treatment, there exists a need to eliminate flames altogether by eliminating an air-gas flame in the post-treatment station as well, and replacing the flame with an alternative that is effective, safe, controllable, capable of being monitored, and otherwise equally as effective as an open flame in post-treatment. It is to the provision of such a replacement system and to a method of post-treating bottles after application of heat transfer labels that the present invention is primarily directed.